Chorionic villus sampling

Definition

Chorionic villus sampling (CVS) is a test done on some pregnant women.

The test is done to screen your baby for genetic problems.

Alternative Names

How the test is performed

CVS can be done through the cervix (transcervical) or through your belly (transabdominal). Miscarriage rates are slightly higher when the test is done through the cervix.

The transcervical procedure is performed by inserting a thin plastic tube through the vagina and cervix to reach the placenta. The provider uses ultrasound images to help guide the tube into the best area and then removes a small sample of chorionic villus tissue.

The transabdominal procedure is performed by inserting a needle through the abdomen and uterus and into the placenta. Ultrasound is used to help guide the needle, and a small amount of tissue is drawn into the syringe. The sample is placed in a dish and evaluated in a laboratory. Test results take about 2 weeks.

How to prepare for the test

Your health care provider will explain the procedure, its risks, and alternative procedures such as amniocentesis.

You will be asked to sign a consent form before this procedure, and you may be asked to wear a hospital gown.

The morning of the procedure, you may be asked to drink fluids and refrain from urinating. Doing so fills your bladder, which helps the doctor see where to best guide the needle.

Tell your health care provider if you are allergic to iodine or shellfish, or if you have any other allergies.

How the test will feel

The ultrasound doesn't hurt. A clear, water-based conducting gel is applied to your skin to help with the transmission of the sound waves. A hand-held probe called a transducer is then moved over the area. In addition, your health care provider may apply pressure on your abdomen to find the position of your uterus.

The cleansing solution will feel cold at first and may irritate your skin if not washed off after the procedure.

Some women say the vaginal approach feels like a Pap smear with some discomfort and a feeling of pressure. There may be a small amount of vaginal bleeding following the procedure.

An obstetrician can perform this procedure in about 5 minutes, after preparation.

Why the test is performed

Some people have a greater risk than others of passing on genetic disorders to their children. A common example is pregnant women over 35.

The test is used to identify any genetic disease in your unborn baby.

Genetic counseling is recommended prior to the procedure. This will allow you to make an unhurried, informed decision about options for prenatal diagnosis.

It can be done sooner in pregnancy than amniocentesis, usually about 10 to 12 weeks of pregnancy.

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